Alteration of epithelial cell lipid synthesis by N-nitrosonornicotine

Changes in the lipid composition of a cell membrane due to the binding of one cell modulator may affect binding of a second modulator, whether that binding is receptor-mediated (specific) or non-receptor-mediated (nonspecific). Such altered binding interactions have been demonstrated in oral epithelial cells, wherein N-nitrosonornicotine (NNN), a nonspecific ligand, enhances phorbol ester binding. To characterize membrane changes that may be responsible for such an effect, the current study examined lipid changes in hamster oral epithelial (HCP) cells associated with NNN binding. HCP cultures at two cell densities, 5 x 10(6) cells/100 mm plate (subconfluent cultures) or 10 x 10(6) cells/100 mm plate (confluent cultures) were incubated in Keratinocyte-Serum-Free Medium and exposed to 10 microM NNN or DMSO (solvent control) for 48 h. Lipids were labeled with 14C-acetate, then extracted, separated by thin layer chromatography, and the 14C-lipids located by autoradiography and counted. Exposure of subconfluent cultures to NNN for 48 h, with 14C-acetate present during the final 24 h, resulted in altered phospholipid and fatty acid labeling. Phospholipid labeling increased slightly in the presence of NNN compared to controls, while fatty acid labeling showed a modest but significant decrease in the presence of NNN. Similar changes occurred in the confluent cultures. Prelabeling of lipids in subconfluent cultures, followed by exposure to NNN in the absence of radiolabel, resulted in significantly (P < 0.05) greater phospholipid labeling in the presence of NNN compared to control cultures. At the same time, fatty acid labeling decreased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)